Optical phase modulation in an injection locked AlGaAs semiconductor laser

Optical phase modulation by injecting coherent CW light into a directly frequency modulated semiconductor laser is reported. Phase modulation was obtained at up to 800 MHz modulation frequency without distortion for a 1.6 GHz full locking bandwidth. A static phase shift of ? took place with a 0.48 mA bias current change in the injection locked laser. Experimental and theoretical results showed that the product of the normalised phase deviation by the frequency deviation and the cutoff modulation frequency is constant.     

Microwave modulation of a quantum-well laser with and withoutexternal optical injection

We compare three microwave modulation methods experimentally and theoretically using a semiconductor quantum-well (QW) Fabry-Perot test laser: (1) direct microwave current modulation of the test laser (electrical modulation); (2) optical modulation by an external single-wavelength pump laser with a modulated optical injection power; and (3) electrical modulation of the test laser that is injection locked by an external single-wavelength pump laser with a constant injection power. This is the first direct comparison of the three modulation methods on the same QW laser, to the best of our knowledge. The bandwidth of optical absorption modulation is 7.7 GHz, which is 1.45 times the direct electrical modulation bandwidth (5.3 GHz) at a bias current of 30 mA in the test laser. On the other hand, the electrical modulation of the test laser under injection-locking condition has a significantly higher modulation bandwidth (10.5 GHz) than both the electrical and optical modulation methods     

Optical phase modulation in an injection locked AlGaAs semiconductor laser

Optical phase modulation obtained by injecting coherent CW light into a directly frequency-modulated semiconductor laser is reported. Phase modulation at up to a 1 GHz modulation frequency has been obtained without compression for a 1.4 GHz half locking bandwidth. Phase deviation can be represented by the ratio of the original FM deviation to the locking half bandwidth. The phase deviation normalized by the frequency deviation is inversely proportional to the cutoff modulation frequency. A static phase shift of π took place with a 0.48 mA drive current change in the injection locked laser. Reduction in FM noise by means of CW light injection and FM noise accumulation in cascaded injection locked laser amplifiers are discussed, together with the optimum design for an injection locked repeater system.     

Magnitude and phase characteristics of frequency modulation in directly modulated GaAlAs semiconductor diode lasers

The magnitude and phase of the small-signal injection current-to-frequency modulation transfer function in GaAlAs semiconductor diode lasers has been measured over the frequency range 100 Hz-1300 MHz using network analyzers. Channeled substrate planar (CSP), buried heterostructure (BH), and crank transverse junction stripe (TJS) laser structures were investigated and will be compared. Approximately 180, 180, and 90° phase differences between the low frequency, thermal frequency modulation (FM), and the high-frequency carrier-density FM was observed for BH, TJS, and CSP laser structures, respectively. The origin of this phase difference and its implications for FM optical communications will be discussed, A rate equation analysis for small-signal injection current modulation (using Mason's flowgraph representation) indicates the presence of a real-axis left half-plane zero in the carrier-density small-signal frequency modulation response. Experimental evidence for this feature has been observed in the measured injection current-to-FM transfer functions.     

Nonlinear dynamics of a laser diode with optical feedback systemssubject to modulation

The nonlinear dynamic behavior of a direct frequency-modulated diode laser with strong optical feedback is examined and compared to a laser diode subject to electro-optically modulated, strong optical feedback. Direct modulation is achieved by sinusoidal modulation of the diode laser injection current. Electro-optic modulation is achieved by applying a sinusoidal voltage to an intracavity phase modulating element. The output state (characterized by the output power versus time, the intensity noise spectrum and the optical frequency spectrum) for both types of modulation is dependent on the ratio of the modulation frequency to the external cavity resonant frequency, and the modulation power. A number of distinct states are observed: conventional amplitude modulation (with FM spectra); multimode, low-noise amplitude modulation; multimode, high-noise amplitude modulation; periodic limit-cycle operation; quasi-periodicity; chaos; low-frequency fluctuations; and mode-locking. There are significant differences between the direct and electro-optic frequency-modulation cases. The onset of the dynamic instability is characterized as a noisy period-one oscillation for direct modulation and a low-frequency fluctuation for intracavity electro-optic modulation. Phase portraits produced experimentally with the use of a digital phosphor oscilloscope are shown to agree well with those constructed from output power versus time data. This represents an experimental method for examining the dynamics phase portraits in real-time     

光纤传感器用半导体激光器光频调制驱动电源

为了实现基于光频调制相位生成载波解调的干涉型光纤传感系统,需要对激光光源的频率进行调制.首先,文章根据直接电流调制原理设计井开发了一种半导体激光器光频调制驱动电源,主要由精密蕈准电压源、内部信号发生器,加法器、恒流源(电压电流转换、电流放大和电压负反馈)、慢启动电路、纹波抑制电路和过流保护电路等基本单元组成.接着,建立...     

Optical repeater using PFM at 1 GHz

We report the first realization of PFM optical communication with a repeater station, using double heterostructure GaAs/GaAlAs semiconductor lasers. The system uses the property of semiconductor lasers for which the optical pulse rate can be locked by an external modulation of the injection current in the vicinity of the resonance frequency of the laser. This modulation scheme has the advantages of a high information rate capability by using the "spiking" resonance of the laser and, more importantly, of a simple repeater station in which another pulsing laser acts as a regenerative pulse amplifier.     

High frequency heterodyne spectroscopy with current-modulated diode lasers

The use of current-modulated semiconductor lasers for optical heterodyne spectroscopy has been investigated at modulation frequencies up to 2.6 GHz. The current modulation produces a simultaneous frequency and amplitude modulation of the laser output. A characteristic heterodyne spectrum occurs when the modulated laser probes a narrow absorption line. In order to analyze the measured spectra, a complete line shape theory has been derived for heterodyne spectroscopy with frequency- and amplitude-modulated laser light. The results show how the obtained signals depend on the modulation frequency and the phase difference between the frequency and the amplitude modulation. The measurement technique permits investigation of the FM-AM phase difference of current-modulated semiconductor lasers.     

Phase locking and chaos synchronization in injection-locked semiconductor lasers

We theoretically studied synchronization of chaotic oscillation in semiconductor lasers with chaotic light injection. Feedback-induced chaotic light generated from a master semiconductor laser was injected into a solitary slave semiconductor laser. The slave laser subsequently exhibited synchronized chaotic output for a wide parameter range with strong injection and frequency detuning within the injection-locking regime. Our numerical simulation revealed that the synchronized slave laser exhibits remarkable phase locking, even for chaotic light injection. Consequently, synchronization in phase fluctuations becomes dominant over intensity fluctuations. We found that there exists a parameter range where the slave can synchronize in phase only, with no intensity synchronization. However, synchronization can be completely destroyed, both in phase and in intensity, when the phase locking becomes unstable due to four-wave mixing or excited resonance oscillation. The phase locking was studied analytically and the correspondence between numerical and analytical results was shown. We also analytically examined chaos synchronization based on a linear stability analysis from the viewpoint of modulation response of injection-locked semiconductor lasers to a chaotic light signal. As a result, we verified that such injection-locking-induced chaos synchronization results from a quasilinear response of the bandwidth-broadened slave laser due to strong optical injection.     

Optical FSK heterodyne detection experiments using semiconductor laser transmitter and local oscillator

Frequency modulated semiconductor laser signals are demodulated by optical heterodyne detection using an independently temperature stabilized semiconductor laser local oscillator and a square-law detector followed by electrical frequency discrimination circuitry. Short-term and long-term beat frequency stability of the free-running laser transmitter and the local oscillator are delineated. Direct frequency modulation characteristics of the laser transmitter are studied by observing the intermediate frequency spectra. Frequency modulation-demodulation of pulse pattern signals at 100-200 Mbit/s is demonstrated. Reduction of the intermediate frequency fluctuation to less than 5 MHz is realized by employing a feedback of the RF frequency discriminator output to the local oscillator injection current.     

GaAlAs semiconductor diode laser 4-ary frequency shift key modulation at 100 Mbit/s

4-ary FSK modulation of a semiconductor diode laser by injection current modulation has been demonstrated at a rate of 100 Mbit/s. The injection current modulator has a modular design which allows expansion to M-ary FSK with independent control of each tone frequency. The design allows considerable flexibility in the logical relationship between the source data and the selected frequency tones.     

General Method for Calculating the Response and Noise Spectra of Active Fabry–Perot Semiconductor Waveguides With External Optical Injection

We present a theoretical method for calculating small-signal modulation responses and noise spectra of active Fabry–Perot semiconductor waveguides with external light injection. Small-signal responses due to either a modulation of the pump current or due to an optical amplitude or phase modulation of the input field can be calculated. Both responses and noise spectra are given through semianalytical expressions taking into account the longitudinal extent and finite end-facet reflectivities of the active device. Different examples of responses and spectra are presented for semiconductor optical amplifiers and an injection-locked laser. We also demonstrate the applicability of the method to analyze slow and fast light effects in semiconductor waveguides. Finite reflectivities of the facets are found to influence the phase changes of the injected microwave-modulated light.      

Frequency modulation on single sideband using controlled dynamics of an optically injected semiconductor laser

Nonlinear dynamics of an optically injected semiconductor laser is applied to photonic microwave generation. By properly adjusting the injection conditions, the optical frequency of the slave laser is first locked to the master laser. The slave laser is then driven into a periodic dynamical state, resulting in a single-sideband (SSB) microwave modulation on the optical carrier. The frequency of the SSB can be controlled by the optical injection strength and detuning. Frequency-modulated SSB can, thus, be obtained from a modulated injection. In this work, we experimentally investigate the generated SSB in terms of its broad tunability and fast modulation response. The results suggest application of this system in radio-over-fiber and optical subcarrier multiplexing technologies when microwave frequency modulation or frequency-shift keying is employed.     

注入锁定法布里-珀罗激光器的单模工作特性

使用分布式反馈(DFB)激光器对法布里-珀罗(F-P)激光器进行单模注入锁定.通过改变F-P激光器的偏置电流,DFB激光器的输出功率以及两激光器间的波长失谐量,对注入锁定F-P激光器的光谱特性、功率特性以及频率响应特性进行实验分析.找出影响注入锁定F-P激光器稳定性的因素,并测量注入锁定F-P激光器的稳定锁定区;通过优化注人条件实现F-P激光器的高边模抑制比(SMSR)输出,最高可达55 dB;通过与自由运转F-P激光器比较,发现注入锁定可以明显抑制半导体激光器在高频调制下光谱的展宽.注入锁定后F-P激光器的3 dB调制带宽接近14 GHz.实验结果表明,通过合理设计光注入条件,注入锁定技术可以明显改善F-P激光器的光谱特性以及高频响应特性,并在高速光纤通信领域中得到广泛应用.     

FM response of quantum-well lasers taking into account carriertransport effects

The FM response of a single-frequency semiconductor laser is very important for communication systems that use direct modulation of the laser injection current. A new rate equation for the optical phase in quantum-well lasers is proposed, and the corresponding FM response is derived. It is shown that the separate-confinement-heterostructure can have a significant effect on the laser performance. The theory is confirmed with experimental results     

On the various time constants of wavelength changes of a DFB laserunder direct modulation

The temporal behavior of the optical frequency emitted by several DFB lasers under direct square wave modulation was measured using an all-fiber implementation of a Mach-Zender interferometer with an imbalance of 30 ps. The impulse response of the optical frequency to injection current modulation was found to contain a time constant as short as 10-20 ns, together with a few longer ones. The existence of such a short time constant is consistent with a thermal analysis of a laser structure with finite thermal impedance of the active region and should be taken into consideration in various wide bandwidth applications of direct modulated semiconductor lasers     

Optical-feedback-induced chaos and its control in multimodesemiconductor lasers

The effects of optical feedback in multilongitudinal mode semiconductor lasers are studied through computer simulations. Two separate regimes are found based on the length of the external cavity. For long external cavities (external-cavity mode spacing larger than the relaxation-oscillation frequency), the laser follows a quasi-periodic route to chaos as feedback is increased. For short external cavities, the laser can undergo both quasi-periodic and period doubling routes to chaos. When the laser output becomes chaotic, the relative-intensity noise is greatly increased (by more than 20 dB) from its solitary-laser value. Considerable attention is paid to the effects of optical feedback on the longitudinal-mode spectrum. The stabilization of the mode spectrum and the reduction of the feedback-induced noise through current modulation are studied and compared with experimental results. Current modulation eliminates feedback-induced chaos when the modulation frequency and depth are suitably optimized. This technique of chaos control has applications in optical data recording     

Polarimetric optical fiber sensor using a frequency stabilizedsemiconductor laser

Improved performance of a polarimetric optical fiber sensor for remote temperature measurement by the use of a frequency-stabilized semiconductor laser is discussed. The temperature change is measured from the phase delay between two orthogonally polarized modes in a polarization-maintaining fiber. The sensor output signal is demodulated utilizing direct modulation of the laser frequency. The center frequency of the modulated laser is locked to a Fabry-Perot interferometer by controlling the injection current. The minimum detectable temperature is evaluated experimentally to be less than 0.005°C, which is several times smaller than that obtained with the free-running laser     

Small signal analysis of optical FM signal amplification by aninjection-locked type semiconductor laser amplifier

A small-signal analysis for optical FM signal amplification by an injection-locked type semiconductor laser amplifier with consideration of the spurious intensity modulation (SIM) is presented. In general, the performance of optical FM signal amplification by a laser amplifier is affected by the value of the injection power, by the performance of the injecting laser (the master laser), and by the difference between the emission frequencies of the master and slave optical cavities. In particular, when the modulation frequency is very low, the output frequency deviation (FD) of the laser amplifier turns out to coincide with that of the master laser. However, SIM of the laser amplifier in this case is influenced by the injection conditions. A suitable definition, the ratio of the output FD to SIM to the input FD to SIM, is given to evaluate the performance of an injection-locked-type semiconductor laser amplifier     

Enhanced Modulation Bandwidth of a Fabry–PÉrot Semiconductor Laser Subject to Light Injection From Another Fabry–PÉrot Laser

Variations in optical spectrum and modulation bandwidth of a modulated Fabry-Perot (FP) semiconductor laser subject to the external light injection from another FP Laser is investigated in this paper. Optimal wavelength matching conditions for two FP lasers are discussed. A series of experiments show that two FP lasers should have a central wavelength overlapping and a mode spacing difference of several gigahertz. Under these conditions both the magnitude and phase frequency responses can be improved significantly.